Method of casting a consumable electrode

ABSTRACT

This invention relates to a method for forming a solid consumable electrode from a plurality of elemental metal constituents, comprising the steps of rolling at least two of the higher melting point constituents into elongated cylindrical shapes with respective different diameters and with different weight proportions, placing said rolled constituents one within the other into an elongated cylindrical mold having a larger inside diameter than the outside diameter of the largest of said rolled constituents, heating a third constituent having a lower melting point than said first two constituents in a separate crucible until it is molten, and pouring said molten third constituent into said mold around and within said first two cylindrcial constituents within said mold to form said consumable electrode, wherein said electrode will have the improved properties of heat conduction and electricity conduction during a subsequent arc-melting of said electrode for producing a homogeneous ingot of alloy having desired weight proportions and chemical properties.

United States Patent Cadden et a1.

[451 Nov. 26, 1974 METHOD OF CASTING A CONSUMABLE ELECTRODE [75] Inventors: Jerry L. Cadden; Donald W.

Hackett, both of Oak Ridge; Fred A. Harris, Knoxville, all of Tenn.

[73] Assignee: The United States of America as represented by the United States Atomic Energy Commission, 'Washington, DC.

Primary Examiner-Francis S. Husar Assistant ExaminerJohn E. Roethel Attorney, Agent, or Firm-John A. Horan; David S. Zachry; Louis M. Deckelmann [5 7] ABSTRACT This invention relates to a method for forming a solid consumable electrode from a plurality of elemental metal constituents, comprising the steps of rolling at least two of the higher melting point constituents into elongated cylindrical shapes with respective different diameters and with different weight proportions, placing said rolled constituents one within the other into an elongated cylindrical mold having a larger inside diameter than the outside diameter of the largest of said rolled constituents, heating a third constituent having a lower melting point than said first two constituents in a separate crucible until it is molten, and pouring said molten third constituent into said mold around and within said first two cylindrcial constituents within said mold to form said consumable electrode, wherein said electrode will have the improved properties of heat conduction and electricity conduction during a subsequent arc-melting of said electrode for producing a homogeneous ingot of alloy having desired weight proportions and chemical properties.

3 Claims, 2 Drawing Figures METHOD OF CASTING A CONSUMABLE ELECTRODE BACKGROUND OF THE INVENTION This invention was made in the course of, or under, a contract with the United States Atomic Energy Commission.

At a US. Government plant, ingots of alloys have been prepared from wrought metals by consumable electrode vacuum melting processes. One of the problems associated with these processes has been consolidation of the alloy constituents into a consumable electrode. The .purity, homogeneity of constituents, and metallurgical properties of alloys are affected by the method of consolidation.

In the consolidation process presently used in the above plant, strips of the elemental constituents (uranium, niobium, and zirconium) are tack-welded to form an electrode. The electrode is then arc-melted in a water-cooled copper cup. The resultant ingot is removed from the cup and arc-melted again to obtain a more homogeneous alloy. By this method, strips of the two minor constituents are trimmed to match the uranium and provide a specific weight of alloy. This creates scrap of the most expensive constituent (niobium). Also, some niobium is scrapped because melting must be stopped well below the bolt-type connection between the electrode and the stinger rod to prevent contamination. In addition, the uranium alloy ingots and sheets fabricated from them are cleaned in nitric acid to remove oxides. The nitric acid cleaning operations are unnecessary with the method of the present invention. Thus, the disposal problems associated with the two nitric acid solutions that were required in the prior method have been eliminated in the present invention.

In other prior art, powder metallurgy techniques are commonly used to consolidate the constituents of an alloy. The powders are consolidated into a desired configuration by compacting and sintering the powder with pressure and heat. However, thepowder metallurgy techniques were not attractive for the program at the above plant for the following reasons: such electrodes have high electrical resistances which inhibit arcmelting operations; the high oxide content of powders make preparation of highly pure alloys difficult; the pyrophoricity of uranium powders creates a potential safety hazard; and alloys having constituents with large density variations tend to segregate. The constituents having greater densities move toward the bottom during mixing and compacting operations.

Thus, there exists a need for a new method for consolidating the elemental constituents of an alloy into a consumable electrode to effect a reduction in the amount of constituent scrap, alleviate the disposal problems associated with nitric acid solutions, and lessen the number of manhours and operations required to produce acceptable ingots of an alloy. The present invention was conceived to meet this need in a manner to be described hereinbelow.

SUMMARY OF THE INVENTION It is the object of the present invention to provide an improved method of consolidating the elemental constituents of an alloy into a consumable electrode with improved melting qualities during a subsequent arcmelting of such an electrode to produce an ingot of the alloy.

The above object has been accomplished in the present invention by casting the constituent having the lowest melting point around selectively spaced and proportioned amounts of the remaining constituents in a suitable mold to form the consumable electrode. The resulting intimate metal-to-metal contact of the surfaces of the higher melting point constituents and the casting constituent almost form a metallurgical bond therebetween. A consumable electrode made in this manner will provide improved conduction of electricity and heat through the electrode during a subsequent arcmelting thereof. This results in a more stable and controllable arc for melting the constituents and forming homogeneous ingots of alloy having uniform physical and chemical properties.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a composite mold and a crucible for fabricating a plurality of consumable electrodes of the present invention; and

FIG. 2 is a cross-sectional view of a composite electrode after casting uranium around rolled strips of Zr and Nb.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The consumable electrodes of the present invention may be formed in a suitable mold such as shown in FIG. 1, for example. The mold of FIG. 1 comprises a housing 2 which is about 36 inches in diameter and about inches in length, and the housing is provided with a plurality of elongated cavities or holes, only holes 3 and 3' being shown in the drawing. There are a total of 14 such holes, for example, in the complete mold and each of these holes has a selected diameter from 3.5 to 4.0 inches. Each of the holes has a respective plug 4, 4, etc. mounted in the bottom thereof, and the housing 2 has a ring support 6 mounted on the bottom thereof for retaining the respective plugs 4 in the bottom of the respective holes 3 during a casting operation to be described hereinbelow.

An inner portion of the housing 2 defines a hollow interior which is closed at its bottom by the ring support 6 and at its top by a plug member 8. The housing 2 is opened at its top and the portion 7 of the housing is shorter than the outside wall of the housing to define an air space such that when a crucible l rests upon the outside wall of the housing 2, a molten constituent of the ultimate consumable electrode is adapted to flow through an aperture 9 in the crucible bottom and then through the air space between the bottom of the crucible and the plug 8 into each of the holes or cavities 3 to form the respective electrodes therein. The tops of the respective holes 3, 3', etc. are covered by means of respective apertured plugs 5, 5', etc.

The present invention has been demonstrated by preparing consumable electrodes from uranium, niobium and zirconium wrought metal.

In atypical casting operation, each of the electrodes in the mold of FIG. I was formed from 109.5 kg of uranium, 9.1 kg of niobium, and 3.1 kg of zirconium. A plurality of niobium strips (48 inchesin length, 5.81 inches in width, and 0.230 inch in thickness) were each rolled into a cylindrical shape about 3 inches in diameter prior to each being positioned in a respective mold cavity 3. Likewise, a plurality of zirconium strips (48 inches in length, 3.56in ches in width, and 0.175 inch in thickness) were each rolled into a cylindrical shape about 2 inches in diameter prior to each being'positioned in a respective mold cavity 3 and within a respective 3-inch diameter niobium roll therein.

With the cylindrical zirconium and niobium shapes properly positioned in the respective mold cavities 3, molten uranium was poured around and into them from the crucible 1. For the casting operation, the crucible containing the uranium was heated to 1,285C in an evacuated furnace. The mold containing niobium and zirconium was heated to 500C at the bottom and l,lC at the top by means not shown. Under these conditions, the molten uranium was poured around the solid strips of rolls of niobium and zirconium in each of the mold cavities 3. The furnace, not shown, for heating the crucible 1 was held at 1,285C for 20 minutes prior to pouring and backfilled with argon 20 minutes after the uranium was poured. The top 2 or 3 inches of each of the resulting consumable electrodes may be cylindrical rolled strips of zirconium and niobium are shown as being symmetrical for the sake of clarity. In actual practice, these rolled strips do not necessarily have to be symmetrical.

It has been determined that consumable electrodes formed in the above-described manner provide for more efficient arc-melting thereof in that during the arc-melting process, the intimate .contact between the constituents of the consumable electrode provides for substantially improved conduction of electricity and heat through the electrode as compared to prior art methods. This results in a more stable and controllable are for melting the constituents and forming homogeneous ingots of alloy having uniform physical and chemical properties. Each electrode may be melted by an electric arc between the strips of the constituent having the highest melting point and the molten pool. The remaining constituents of the electrode are melted by the heat induced in the arcing constituent.

The following table gives the chemical analysis of first and second melts prepared from four electrodes, formed in the above-described manner-The four ingots formed in the first melt were 5 inches in diameter and after top and bottom sections thereof were removed for chemical analysis, the remaining portions were welded together for the second melt to form an ingot 7 inches in diameter, and different sections were cut therefrom ble.

TABLE CHEMICAL ANALYSIS OF FIRST AND SECOND MELT INGOTS Ingot No. Uranium Niobium Zirconium Copper Iron Carbon Hydrogen Nitrogen Oxygen Location (PP (pm) (pm) (pm) (pm) (ppm) (First Melt) I944 Top 89.27 7.84 2.48 46 Bottom 89.05 8.06 2.57 10 20 85 I940 Top 89.72 7.73 2.43 6 7 33 4 6 47 Bottom 89.37 7.83 2.63 7 33 49 3 4 43 1934 Top 89.51 7.90 2.58 10 20 43 S 5 70 Bottom 89.13 7.91 2.62 8 20 6 I5 76 I936 Top 89.44 7.76 2.57 5 28 50 3 ll 71 Bottom ,7 88.79 8.36 2.83 10 26 99 3 l3 7] (Second Melt) Top 89.33 7.88 2.67 2 36 6" 20" 76 Mid-Top 89.25 7.90- 2.63 2 25 32 6 12 73" Middle 88.98 8.14 2.70 2 25 46 7 [5 61 Mid-Bottom 88.93 3 4 2 25 2 121 m m Bottom 89.47 7.78 2.56 2 30 54 4" 13" 46" 6I2l [2(2\ 52(2) Center-Middle 88.04 8.77 2.83 10 25 92 Drilled "Edge. Center.

an extension of the uranium casting beyond the more expensive strips of zirconium and niobium. Thus, the clamped portion of each electrode for a subsequent arc-melting operation, which portion is subsequently discarded, will be less expensive uranium.

A typical cross-section of an electrode formed in th above manner is shown in FIG. 2 of the drawing. The

It can be seen from the results shown in the above table that there is very little variation in the chemical properties of the ingots formed in the first melt, or between those properties and chemical properties of the ingot formed in the second melt. Thus, it should be evident that the consumable electrodes formed bythe -method of the present invention, as described above, provide for improved conduction of heat and electricity through the electrodes when they are subsequentially used for vacuum arc-melting to produce ingots of alloy. Also, homogeneous ingots of alloy having uniform physical and chemical properties can be produced by the improved consumable electrodes of the present invention.

for chemical analysis which results are shown in the ta- It should be understood that the present method is not limited to the use of the specific metals described above in forming the consumable electrodes. It can be equally utilized with any other combination of desired metals to form consumable electrodes for subsequent arc-melting to form ingots of other desired alloys.

This invention has been described by way of illustration rather than by limitation and it should be apparent that it is equally applicable in fields other than those described.

What is claimed is:

l. A method for forming a solid consumable electrode from a plurality of elemental metal constituents, comprising the steps of rolling at least two of the higher melting point constituents into elongated cylindrical shapes with respective different diameters and with different weight proportions, placing said rolled constituents one within the other into an elongated cylindrical mold having a larger inside diameter than the outside diameter of the largest of said rolled constituents, heating a third constituent having a lower melting point than said first two constituents in a separate crucible until it is molten, and pouring said molten third constituent into said mold around and within said first two cylindrical constituents within said mold to form said solid consumable electrode, said first two constituents being respectively zirconium and niobium, and said third constituent being uranium, whereby said electrode will have the improved properties of heat conduction and electricity conduction during a subsequent arc-melting of said electrode to produce an ingot of alloy having desired weight proportions and chemical properties.

2. The method set forth in claim 1, wherein the smallest diameter rolled constituent is the zirconium and the largest diameter rolled constituent is the niobium, and the weight proportions of said electrode constituents are 109.5 kg of uranium, 9.1 kg of niobium, and 3.1 kg of zirconium.

3. The method set forth in claim 1, wherein said third constituent was heated to 1,285C in said crucible prior to said pouring step, and said mold was heated to 500C at the bottom thereof and to l,lO0C at the top thereof prior to said pouring step. 

1. A METHOD FOR FORMING A SOLID CONSUMABLE ELECTRODE FROM A PLURALITY OF ELEMENTAL METAL CONSTITUENTS, COMPRISING THE STEPS OF ROLLING AT LEAST TWO OF THE HIGHER MELTING POINT CONSTIT UENTS INTO ELONGATED CYLINDERICAL SHAPES WITH RESPECTIVE DIFFERENTS DIAMETER AND WITH DIFFERENT WEIGHT PROPORTIONS, PLACING SAID ROLLED CONSTITUENTS ONE WITHIN THE OTHER INTO AN ELONGATED CYLINDERICAL MOLD HAVING A LARGER INSIDE DIAMETER THAN THE OUTSIDE DIAMETER OF THE LARGEST OF SAID ROLLED CONSTITUENTS, HEATING A THIRD CONSTITUENT HAVING A LOWER MELTING POINT THAN SAID FIRST TWO CONSTITUENTS IN A SEPARATE CRUCIBLE UNTIL IT IS MOLTEN, AND POURING SAID MOLTEN THIRD CONSTITUENTS INTO SAID MOLD AROUND AND WITHIN SAID FIRST TWO CYLINDRICAL CONSTITUENTS WITHIN SAID MOLD TO FORM SAID SOLID CONSUMABLE ELECTRODE, SAID FIRST TWO CONSTITUENTS BEING RESPECTIVELY ZIRCONIUM AND NIOBIUM, AND SAID THIRD CONSTITUENTS BEING URANIUM, WHEREBY SAID ELECTRODE WILL HAVE THE IMPROVED PROPERTIES OF HEAT CONDUCTION AND ELECTRICITY CONDUCTION DURING A SUBSEQUENT ARCMELTING OF SAID ELECTRODE TO PRODUCE AN INGOT OF ALLOY HAVING DESIRED WEIGHT PROPORTIONS AND CHEMICAL PROPERTIES.
 2. The method set forth in claim 1, wherein the smallest diameter rolled constituent is the zirconium and the largest diameter rolled constituent is the niobium, and the weight proportions of said electrode constituents are 109.5 kg of uranium, 9.1 kg of niobium, and 3.1 kg of zirconium.
 3. The method set forth in claim 1, wherein said third constituent was heated to 1,285*C in said crucible prior to said pouring step, and said mold was heated to 500*C at the bottom thereof and to 1,100*C at the top thereof prior to said pouring step. 